/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.support;

import org.springframework.lang.Nullable;
import org.springframework.web.servlet.FlashMap;
import org.springframework.web.util.WebUtils;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;

/**
 * Store and retrieve {@link FlashMap} instances to and from the HTTP session.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.1.1
 */
public class SessionFlashMapManager extends AbstractFlashMapManager {

    private static final String FLASH_MAPS_SESSION_ATTRIBUTE = SessionFlashMapManager.class.getName() + ".FLASH_MAPS";


    /**
     * Retrieves saved FlashMap instances from the HTTP session, if any.
     */
    @Override
    @SuppressWarnings("unchecked")
    @Nullable
    protected List<FlashMap> retrieveFlashMaps(HttpServletRequest request) {
        HttpSession session = request.getSession(false);
        return (session != null ? (List<FlashMap>) session.getAttribute(FLASH_MAPS_SESSION_ATTRIBUTE) : null);
    }

    /**
     * Saves the given FlashMap instances in the HTTP session.
     */
    @Override
    protected void updateFlashMaps(List<FlashMap> flashMaps, HttpServletRequest request, HttpServletResponse response) {
        WebUtils.setSessionAttribute(request, FLASH_MAPS_SESSION_ATTRIBUTE, (!flashMaps.isEmpty() ? flashMaps : null));
    }

    /**
     * Exposes the best available session mutex.
     *
     * @see org.springframework.web.util.WebUtils#getSessionMutex
     * @see org.springframework.web.util.HttpSessionMutexListener
     */
    @Override
    protected Object getFlashMapsMutex(HttpServletRequest request) {
        return WebUtils.getSessionMutex(request.getSession());
    }

}
